The invention concerns heating of hydrocarbon materials in geological subsurface formations by radio frequency (RF) electromagnetic fields and more particularly this invention provides a method and apparatus for heating mixtures containing bituminous ore, oil sands, oil shale, tar sands, or heavy oil by RF energy emitted by well casings that are coupled to an RF energy source.
Extraction from heavy oil reservoirs including oil sands deposits, shale deposits and carbonate deposits, requires heating of the deposits to separate hydrocarbons from other geologic materials and to maintain hydrocarbons at temperatures at which they will flow. One common known method of heating such deposits is known as steam assisted gravity drainage or SAGD. In SAGD, two parallel horizontal wells are drilled vertically adjacent to each other in a formation. The upper well is an injection well and the lower well is a production well. Steam is first introduced into both wells to heat heavy oil adjacent to the wells. Heavy oil drains into the production well creating a porous formation through which steam permeates outwardly to heat the formation. When heated oil can flow from the injection well to the production well, steam injection into the production well is stopped. Steam is injected into the injection well to heat a larger region surrounding the wells to continue extraction of heavy oil.
Among the disadvantages of SAGD is the addition of water to the materials which requires a large amount of energy to remove. For both environmental reasons and efficiency/cost reasons it is advantageous to reduce or eliminate the amount of water used in processing bituminous ore, oil sands, oil shale, tar sands, and heavy oil, and to provide a method of heating that is efficient and environmentally friendly and that is suitable for post-excavation processing of the bitumen, oil sands, oil shale, tar sands, and heavy oil. Many bitumen resources may be too shallow or with insufficient caprock for steam enhanced recovery.
Prior RF heating applicators, for heavy oil in subsurface formations have typically been vertical dipole like antennas. U.S. Pat. Nos. 4,140,179 and 4,508,168 disclose such prior dipole antennas positioned within vertical wells in subsurface heavy oil deposits to heat those deposits. Arrays of dipole antennas have been suggested to heat subsurface formations. U.S. Pat. No. 4,196,329 discloses an array of dipole antennas that are driven out of phase to heat a subsurface formation. Thus, prior systems for heating subsurface heavy oil bearing formations by RF has generally relied on specially constructed and structurally complex RF emitting structures that are positioned within a well.